1. Field of the Invention
The present invention relates to an image reading method and apparatus, in which light from a light source is irradiated on a transmission original or a reflection original through a slit, and the transmitted light or reflected light is read by a solid-state image pickup device.
2. Description of the Related Art
As a method for reading an original image, there is known a method in which slit light, whose longitudinal direction coincides with a main scanning direction, is irradiated on an original image and is moved in a sub-scanning direction perpendicular to the main scanning direction, and light reflected by or transmitted through the original image is guided to a solid-state image pickup device (CCD sensor) via a lens, thereby allowing reading of the original image.
The slit width of the slit light is usually larger than the read width of a CCD sensor. The distribution of the amounts of slit light is set so that light reflected by a reflector which covers the back of a light source is made convergent at one point, and therefore, the distribution is formed as a so-called Gaussian distribution having a relatively sharp peak.
For this reason, during sub-scanning movement, the position where the slit light is irradiated is displaced due to vibration and the like, and the amount of light may vary within the range of the read width of the CCD sensor.